1. Field of the Invention
The present invention relates in general to an image forming apparatus. More specifically, the invention relates to an electronic copying machine which is capable of designating any part of the original document image and erasing that part by comparatively simple construction and operation.
2. Description of the Related Art
A demand has arisen recently for the development of an image forming apparatus with a facility for editing the document image original which it copies. In particular, there is a strong demand for the development of a facility for omitting on the copy the unwanted part of a document image original.
One image forming apparatus has already developed which fulfils this requirement (U.S. Pat. No. 4,215,929, Sato et al.). This existing image forming apparatus consists of a light source which applies an image area control light which controls the formation of the electrostatic latent image on a photosensitive body by cutting off or applying light in association with the exposure of the document image original, a mask member which controls the said control light to a desired width by superposition, and a control means for controlling the working of this mask member. The aim here is to control the formation of the electrostatic latent image by the difference between the two operations, whereby the control light mentioned above is either transmitted or masked, and thus to obtain an image of the required area of the document image original. Depending on the way in which the mask member is superposed, either an image of a part of the document image original can be obtained, or the part can be erased and an image obtained of the remainder.
Further, this existing image forming apparatus is provided with a monitoring means which displays the document image original, and a position determining means, which in association with this monitoring means selects as desired that area of the document image orignal which is required. By controlling the mask member in association with the position determining means, the required area of the document image original can be selected at will as the document image original is displayed, and an image of that area obtained.
However, the existing image forming apparatus as disclosed in U.S. Pat. No. 4,215,929 has the following drawbacks.
(1) Mechanical parts, such as a motor and gears, are required to shift the mask member between the single and the superposed state, and this makes the apparatus complicated. Also, there is a strong possibility that in use over a long period the mask member will become deformed, making accurate masking impossible.
(2) The monitoring means consists of a lamp for irradiating the document, a mirror and lens for directing the light reflected from the document, and a screen on which the image of the document is projected. This monitoring means is provided separate from the document table which is provided, above the photosensitive body, for the exposure of the document. Space is therefore required for the provision of this monitoring means, and this increases the overall size of the image forming apparatus.